Frost collector for refrigerated display cases



Aug. 1, 1967 J, H. BRENNAN 3,333,437

FROST COLLECTOR FOR REFRIGERATED DISPLAY CASES Filed Aug. 5, 1965 2 Sheets-Sheet 2 INVENTOR. JAMESH BRENNAN MWS Q ATTORNEYS United States Patent 3,333,437 FROST COLLECTOR FOR REFRIGERATED DISPLAY CASES James H. Brennan, Trenton, N.J., assignor to Emhart Corporation, Bloomfield, Conm, a corporation of Connecticut Filed Aug. 3, 1965, Ser. No. 476,808

4 Claims. (Cl. 62-256) This invention relates generally to refrigerated display cases of the commercial type, used in supermarkets and similar establishments for the purpose of holding a large quantity of refrigerated foods in an attractively displayed arrangement and at a temperature below freezing.

More particularly, the invention has reference to a device usable either as a built-in component of, or as a separate accessory to, a case of the type described, and serving as a collector of frost that would otherwise be deposited directly upon the refrigerating mechanism of the display case.

By way of background, it may be observed that a continuing problem, in the manufacture and operation of display cases at temperatures below freezing, resides in the fact that air that is being returned to the refrigerating mechanism for recooling is already at a temperature below freezing and as a result any moisture carried thereby is in the form of a super-cooled liquid or is carried by the air in the form of entrained crystals of ice or frost. In either case the moisture and crystals are deposited in the form of frost or snow upon the refrigerated coiling and other surfaces incorporating in said mechanism and contacted by the low temperature return air.

The deposition of such frost or snow is found to take place on various surfaces and at various points which serve to provide a nucleus, or crystallization initiating, or seeding point or surface. Moreover such accumulations take place even though the points or surfaces where snow or frost deposit are at temperatures which are the same or even higher than the temperature of the super-cooled moisture or the crystal containing air coming into contact therewith. The temperatures at which the formation of frost or snow will occur must be below freezing (32 F.) but tend to vary considerably depending upon numerous conditions which are little understood but are discussed at length in an article by B. J. Mason appearing in the Scientific American, January 1961 at pages 120 to 131 and on pages 119 to 150 of a book entitled, The Art and Science of Growing Crystals, by J. J. Gilman, published by John Wiley & Sons, Inc.

Further as found by experience, and as pointed out in the foregoing publications, the form of the crystals deposited is subject to wide variation. However, at the temperatures presented in the operation of refrigerated cases used in the preservation and display of ice cream, frozen foods, and the like, the crystals produced are generally in the form of long fine needles which project outwardly from the surfaces or points on which they accumulate so as to obstruct the passages and limit the flow of air through the passages.

In actual practice, and particularly on multideck equipment (although the problem exists in any type of low temperature equipment in the general category specified), where large volumes of air are handled for refrigeration purposes, the problem of frost accumulation in the return air flue and on the coiling surfaces, becomes quite serious. The progressive and relatively rapid accumulation of frost, particularly in these areas, results in a corresponding, progressive reduction in the volume of air that is circulated within the fixture. Consequently, the refrigerating action is seriously diminished, and frequent defrosting cycles must be re- 3,333,437 Patented Aug. 1, 1967 sorted to for the purpose of controlling the condition and maintaining flow of air in the desired pattern at a predetermined minimum of volume.

It is reasonable to assume, accordingly, and in fact it has been long recognized in the industry, that an increase in the length of time that one can maintain the air pattern, resulting from a reduction in the number of defrost cycles and/or a reduction in the time required for each of these cycles means increased operating efficiency of the refrigerating system proper.

The main object of the present invention is to reduce the number and/or the individual length of the defrost periods mentioned above. To accomplish this, I provide a device mountable in the return air flue of the low temperature refrigerated display case, which includes a grid composed of a metal frame onto which an electrical resistance element is laced. The resistance element and the frame thus cooperate to provide a grid means, of fiat, generally rectangular configuration, adapted to be mounted in a slightly tilted position in the return air flue, in contact with opposite walls of said flue. By reason of this arrangement, this device extends across the path of air moving through the line, in a position such as to require that all the air that is so moved be channeled through interstices or openings in the grid, before impinging upon the re-frigerated coiling surfaces of the cooling mechanism of the case. As the low temperature return air passes through the openings of the grid, supercooled moisture and ice crystals with which the air is laden are caused to -be deposited upon the grid in the form of frost. The frost so deposited upon the grid is frost that would otherwise have been deposited upon the refrigerated coiling surfaces of the cooling mechanism, and hence there is a substantial reduction in the build-up of frost or snow accumulation upon the cooling unit itself.

This in turn results in a reduction in the number of defrost periods, by reason of the fact that the frost collector constituting the present invention is defrosted by a separate control mechanism, operating completely independently of the cooling unit and any defrost means associated therewith.

The separate defrosting of the collector means briefly described above may be and preferably is automatically responsive to a timing device or the like, and is designed to defrost the collector to, but not beyond, a point where the frost actually changes state and liquefies. In this way the bulky and needle-like frost or ice crystals are caused to melt and collapse into the form of droplets of water which tend to adhere to the wires or elements of the grid. The frost obstruction developed within the return air duct is thereby eliminated without vaporizing the liquid or causing it to migrate or be transferred into contact with the coils, fins or surfaces of the evaporator to form ice or frost thereon. Thereafter, during the periodic defrosting cycle of the refrigerating unit, the resultant warming of air in the circulating air pattern is effective to completely clean the frost collecting device as well as the refrigerated coiling surfaces, with the liquid condensate from both of these assemblies being drained off in the usual manner.

Among more particularobjects of the invention are the following:

To provide a device of the character stated that will be designed to be either built into display case construction designed for operation at temperatures below freezing at the time of original manufacture, or alternatively, to be manufactured and sold as a separate accessory, capable of installation in display cases already in use;

To so design the device that when used as an accessory in the manner described above, it can be installed quickly and easily, Without modification of the display case;

To provide a device of the character stated that will be self-contained, so that whether it is built into a low temperature refrigerated display case during the original manufacture of said case, or is instead sold as an accessory for installation in such cases already in use, it will neither affect or be alfected by the wiring or other component parts of said case;

To incorporate in the construction of the frost collector a design that will produce a uniform build-up of frost on the deposition surfaces of the collector, in such a way as to maintain maximum flow of air through the interstices of the collector until said build-up has progressed to a point where it covers substantially the entire surface area of the grid; and

To provide a collector as stated that will be efficient in use, will be simple and inexpensive in design, capable of installation by relatively unskilled help, and rugged and trouble-free when in use.

Other objects will appear from the following description, the claims appended thereto, and from the annexed drawings, in which like reference characters designate like parts throughout the several views, and wherein:

FIG. 1 is a transverse sectional view through a typical, conventioal low temperature refrigerated display case, with the frost collector constituting the present invention being mounted in operating position therein, said frost collector being shown in end elevation;

FIG. 2 is a sectional view substantially on line 2-2 of FIG. 1;

FIG. 3 is an enlarged perspective view of the device, portions being broken away, the wiring of the device constituting the present invention being illustrated partly diagrammatically;

FIG. 4 is an enlarged transverse sectional view through the device substantially on line 44 of FIG. 3; and

FIGS. 5 and 6 are fragmentary, transverse sectional views through the return air flue, showing the manner in which frost progressively accumulates upon the collector.

Referring to the drawing in detail, as has been previously noted herein, the invention is particularly well adapted for use on multi-deck equipment operating at temperatures below freezing, since such equipment involves the handling of especially large volumes of air. The greater the air volume handled by the equipment, the greater is the frost accumulation and defrost problem, and hence the more important is the provision of a frost collector such as will be described in detail herein.

Nevertheless, the invention is adapted for use on any of various types of refrigerated display equipment, which operates at temperatures below freezing, and by way of example has been shown in FIG. 1 as incorporated in a case of the type used for the merchandising of frozen foods and ice cream. It will be understood that this showing is intended to be merely illustrative of a wide variety of. low temperautre refrigerated cases in which the invention can be readily incorporated.

In the illustrated example, the display case has been generally designated 10 and has an upwardly opening food compartment 11 defined by front, back, bottom, and end walls 12, 14, 16 and 18 respectively. Inwardly from the front, back, and bottom walls are flue walls 20, 22 and 24 respectively, defining a duct 25 extending continuously .along the front, bottom and back walls, between said walls and the food compartment 11.

This duct includes the usual return air flue 26, bottom flue 28, and back or outlet flue 30. As shown by the flow arrows, air circulates within these flues, in a continuous, closed air pattern, with said air being discharged from the upper end of the outlet flue 30, for movement across the open top of the compartment 11 as shown at 32, the return air entering the return air flue 26 at the upper end thereof, and moving downwardly for recooling by the refrigerating unit mounted in the bottom flue. In the illustrated, typical construction, there is provided a ticket moulding 34, projecting forwardly from the rear sill 35 above outlet louvers 36, through which the cooled air is discharged for movement across the open side of the compartment. Also provided in the conventional construction shown is the usual front trim moulding 38, having inlet 40 for the return air entering the return or intake air flue 26.

In a typical display case as shown, the desired rigidity is imparted to the walls of the various flues by such means as upper and lower Z-brackets 42, 44 respectively. These are held in position in any suitable manner, and are swiftly and easily inserted or removed.

Incorporated in the display case (in the present instance in the bottom flue,) is a refrigerating mechanism generally designated 45, including in the illustrated example evaporators 46, 48, between which is provided a fan 50 for maintaining air circulation in the desired pattern. The refrigerating mechanism employed is of such size or capacity, or is so operated that the temperature maintained within the food compartment and the temperature of the .air circulated about said compartment and through the return air flue 26 by the fan 50 are low temperatures which term as used herein refers to temperatures below freezing (32 F.). In the bottom surface of the flue 28, there is also provided the conventional drain pan 52 which extends longitudinally of the display case, and which has the outlet 54.

It is also conventional to provide, as a component of a typical display case such as shown, a rubber sleeve 56, communicating between the bottom flue 28 and the space below the insulated bottom wall 16, to provide a conduit through which the lines extending to and from the refrigerating mechanism 45 can be led. Said lines are not shown in the illustrated example, since they are not necessary to description of the invention and the parts of the display case cooperating therewith.

At the juncture between the front and bottom walls 12, 16 respectively, there is provided a raceway 58 extending longitudinally of the display case to provide a conduit for the electrical cable or cables 60 needed to wire the display case.

All this is conventional construction, and has been illustrated and described herein merely for the purpose of showing the environment and the cooperating components associated with the invention. The invention has been generally designated '62, and includes a grid generally designated 63 (see FIG. 2). Grid 63 comprises in its principal features of construction, a frame generally designated 64, and a resistance element.

The frame 64 is of generally rectangular configuration, and can be of any desired height and length, according to the size of the particular display case in which the collector is to be used, as well as the type of such display case. It is mainly important that the length of the frost collector be such as to cause all or the greatest part of air, passing through the return air flue, to be channeled through interstices or openings defined in the grid 63.

In the illustrated example, I provide a series of uniformly spaced transverse rails 66 formed of rigid rod stock. Spot-welded or otherwise fixedly secured to the rails 66, in crossing relation thereto, are longitudinal rails 68.

The grid, as above noted, also includes a resistance element. This has been designated 70, and in a preferred embodiment is laced back and forth between the rails 66 disposed at the opposite ends of the frame. The resistance element itself constitutes a deposition surface for frost, and the various courses of the laced element cooperate with one another and with the frame 64 in defining openings 71 through which air may pass as it is moved through the return air flue.

To facilitate the lacing of the element upon the frame, I provide in the illustrated example a series of uniformly spaced metal pins 72, secured to one of the end rails 66 (see FIG. 2), and projecting outwardly from said one rail to provide means about which the element can be laced. In the illustrated example, the lacing proceeds just below the upper one of the rails 68. Starting at this point, the resistance element 70 is extended along one face of the frame to the other end rail 66, after which it is coiled about the rail 66 remote from pins 72, in an inclined path as shown at 73 in FIG. 4. Then, the resistance element is extended back along the opposite face of the frame, and is coiled about the rail 66 having the pins 72. It is now extended along the first mentioned face of the frame, so that as the lacing proceeds in the manner described, there are provided, on the respective, opposite faces of the frame, open webs of the laced resistance element, composed of spaced, parallel courses of said element. In this way, there is a substantial number of deposition surfaces for the frost, and at the same time, the grid is fully opened to the passage of air therethrough.

Referring to FIG. 3, provided upon the opposite ends of the resistance element 70 are rubber-covered electrical connectors 74, permitting connection of the ends of the element to the opposite leads 75 of (FIG. 1) an insulated conductor 76. In accordance with the invention, the rubber sleeve 56 is utilized as a passage whereby the conductor 76 can extend out of the duct, and into the raceway 58. Within the raceway, the conductor is connected in circuit (FIGS. 1 and 3) with a timer 78 or other automatic control device. The timer has connections 79 permitting it to be attached to a source of electrical power. In the illustrated example, the connections 79 are spliced or otherwise electrically connected to the cable 60 of the display case, at a location such that the timer is preferably unaffected by, and does not itself affect electrical devices within the case to which power is supplied by means of the cable 60'.

In use of the device, it is readily installed in a low temperature refrigerated display case that is already in use, merely by removing the upper Z-brackets 42, after access thereto is provided by removal of any necessary trim such as the moulding 38. One merely inserts the grid, allowing the same to rest upon the lower Z-brackets 44 (see FIGS. 1 and 2). When this is done, the grid will automatically assume an inclined position as shown in FIG. 1, in which the grid is in contact, .at its upper and lower ends, with wall 12 and wall 20, respectively. The grid thus extends across the return air flue, in a position such that for all practical purposes, all air that is moving through the return air flue must pass through the grid openings. The result is that super-cooled moisture with snow or ice crystals with which the air is laden at the time it is fed back through the return air flue for recooling, is caused to be deposited on the frame and resistance element of the grid in the form of frost or snow and in advance of the evap-orators 46 and 48.

This would be frost that would otherwise have been carried on into bottom flue 28 and deposited upon the evaporators 46, 48 and other components of the refrigerating mechanism 45 disposed in the path of air flowing in the circulating air pattern of the display case. Therefore, the requirement for defrosting of the refrigerating coiling surfaces of mechanism 45 is lessened, so that defrost periods for said mechanism become more infrequent. This obviously has the effect of increasing the over-all efliciency of the display case, in that there is markedly less impedance of air flowing in the refrigerating air pattern previously described herein.

In any event, in accordance with the invention the periodic defrosting of the collector 62, necessitated by frost deposition on the grid 2 in excessive degree, is effected without necessity of shutting down the refrigerating cycle or interfering in any other way with the normal cooling and circulation of the air within the case. 1 accomplish this by the provision of any suitable automatic control on the frost collector, as for example the timer 78. In a typical example, I may defrost the collector on the average of once every hour, for a period of about two minutes. During this period the resistance element may, for example, be supplied with current in an amount equal to 10 watts per foot of the resistance element, or in a typical frost collector of the type illustrated which is 4 feet in length the resistance element may be supplied with 900 watts of current at 212 volts. The resistance elements of such a frost collector, operated as described, in a display case loaded with frozen food, and contacted by air in the return air duct having a temperature of 0 F., was found to attain temperatures as indicated in the following table:

In this way, I defrost the collector only to an extent that will change the state of the accumulated frost, from solid to liquid. The defrost period is not allowed to continue to a point such as would vaporize the liquid, since this would have the undesirable result of merely causing migration of the moisture from the collector to the refrigerating mechanism.

Rather, when the defrost of the collector occurs, it takes place without regard to any defrosting of the refrigerating mechanism itself. The defrosting of the mechanism 45 might and often will occur at a time when the defrosting of the collector is taking place, but it is not significant that it does so.

When the state of the accumulated moisture on the collector is changed to a liquid, said liquid tends to remain upon the collector, although a. few drops might tend to fall therefrom for flow into the drain pan 52. Though the moisture is still upon the collector in its liquid state, however, it does not interfere with the free passage of air through the openings of the grid.

Eventually, the defrost means (not shown) of the refrigerating unit or mechanism 45 operates in the usual fashion, although as previously noted herein such operation will be less frequent when the invention is used. It is considered that the defrost means of the refrigerating mechanism will operate every four or six hours, at a typical installation for perhaps twenty-two to thirty minutes. When this operation occurs, air circulated in the duct is increased in temperature to a predetermined maximum at the return air duct intake openings 40, as for example 47 F.

This provides an air curtain extending across the open side of food compartment 11, which is lower than ambient, so as to minimize the migration of ambient air into the pattern. At the same time, this temperature is such as to completely clean the frost collector grid, as well as the coiling surfaces of the refrigerating mechanism 45, of all accumulated moisture. Said moisture drains off both from the grid and from the refrigerating mechanism components, in to the pan 52.

It is important to note, as shown in FIGS. 5 and 6, that the deposition of the frost F upon the grid proceeds in a manner such as to maintain interference with free air movement at a minimum, until the deposition of the frost occurs to a point such as to make defrosting advisable. The first portion of the collector grid that is impinged upon by super-cooled moisture and ice crystal containing air entering the return flue is the top portion thereof. Accordingly, fro-st or snow is deposited upon this top portion, and builds up to a predetermined thickness, more or less. When this occurs, the openings at the top of the device will either be completely closed or will at least be reduced substantially in size by the bulky needle-like crystals which have accumulated on the upper portion of the frost collector. As a result, air passing through the return duct now tends to move below the 7 area in which the frost has accumulated, and still passes freely through the openings of grid areas that are still unaffected.

The frost accumulation tends to move downwardly, progressively, from the top, as shown by a comparison of FIGS. and 6. As it moves downwardly, it builds up to the predetermined thickness before additional frost of any consequence is deposited upon other, lower areas of the grid through which air still passes freely. This progressive accumulation of frost continues, until eventually the passage of air through the openings of the grid is impeded to an excessive degree, and would affect adversely the efliciency of the refrigerating action and the accompanying air circulation. At this time, the timer, which is pre-set to close a circuit to the resistance element at what is found to be the most desirable time according to the particular installation, operates to close said circuit. Current is thus passed through the resistance element, and the above-described change of the state of the accumulated bulky ice crystals to drops of liquid, occurs. This completely opens the grid to the passage of air once again, all without interfering with the circulation of refrigerated air through the display case.

It is also believed worthy of note at this point that in the illustrated example, the device is shown as a selfcontained, quickly installable accessory to refrigerated cases already in use. It could, with equal case, be built into a refrigerated display case, and in fact when built in in this way, need not be changed in design in any way, should the manufacturer so prefer. As an accessory, it is installed quickly, by relatively unskilled help. In fact, it is quite possible to provide a conventional attachment plug cap upon the conductor 76, and plug the device into a near-by convenience outlet, without even having to splice the conductor into the wiring of the display case.

It is believed apparent that the invention is not necessarily confined to the specific use or uses thereof in low temperature refrigerated display cases described above, since it may be utilized in any type of low temperature refrigerated equipment to which it may be suited. Nor is the invention to be necessarily limited to the specific construction illustrated and described, since such construction is only intended to be illustrative of the principles of operation and the means presently devised to carry out said principles, it being considered that the invention comprehends any changes in construction that may be permitted within the scope of the appended claims.

I claim:

1. In low temperature refrigerated equipment having a storage space therein provided with an access opening,

means for forming an air curtain directed across said access opening and including duct means having an air outlet at one side of said access opening and a return air duct at the opposite side of said access opening, means for circulating air in a substantially continuous circuit through said duct means and outlet to said return air duct to establish said air curtain, refrigerating means including an evaporator located in said duct means and operable during a refrigerating cycle to maintain the air circulated through said duct means and across said access opening and through said return air duct at a temperature below freezing, the improvement comprising means for reducing the accumulation of frost on said evaporator comprising a non-refrigerated frost collector located in said return air duct and in advance of said evaporator for accumulating frost thereon, means for converting frost accumulated on said frost collector from a solid to a liquid form without substantial vaporization of the liquid produced including heating means operable periodically to raiseithe temperature of said frost collector to a temperature above freezing for a limited time and to an extent sufficient only to convert the accumulated frost into drops of water without causing vaporization thereof and migration of moisture from said frost collector to said evaporator, said heating means being operable at least at times during said refrigerating cycle.

2. Low temperature refrigerated equipment as defined in claim 1 wherein said frost collector embodies a grid comprising a frame having electrical resistance elements thereon.

3. Low temperature refrigerated equipment as defined in claim 1 wherein said frost collector embodies a frame located in an inclined position within said return air duct and has a plurality of vertically spaced substantially horizontal electrical resistance elements thereon to which said drops of water tend to cling.

4. Low temperature refrigerated equipment as defined in claim 1 wherein said heating means is controlled by a timer.

References Cited UNITED STATES PATENTS 2,663,158 12/1953 Sanders 62-283 X 2,923,135 2/1960 Preotle 62-283 X 3,063,256 11/1962 Lamb 62-283 X 3,096,629 7/ 1963 Rembold 62283 3,233,424 2/1966 Vogel 6'2--283 3,243,971 4/ 1966 Beckwith 62-256 MEYER PERLIN, Primary Examiner. 

1. IN LOW TEMPERATURE REFRIGERATED EQUIPMENT HAVING A STORAGE SPACE THEREIN PROVIDED WITH AN ACCESS OPENING, MEANS FOR FORMING AN AIR CURTAIN DIRECTED ACROSS SAID ACCESS OPENING AND INCLUDING DUCT MEANS HAVING AN AIR OUTLET AT ONE SIDE OF SAID ACCESS OPENING AND A RETURN AIR DUCT AT THE OPPOSITE SIDE OF SAID ACCESS OPENING, MEANS FOR CIRCULATING AIR IN A SUBSTANTIALLY CONTINUOUS CIRCUIT THROUGH SAID DUCT MEANS AND OUTLET TO SAID RETURN AIR DUCT TO ESTABLISH SAID AIR CURTAIN, REFRIGERATING MEANS INCLUDING AN EVAPORATOR LOCATED IN SAID DUCT MEANS AND OPERABLE DURING A REFRIGERATING CYCLE TO MAINTAIN THE AIR CIRCULATED THROUGH SAID DUCT MEANS AND ACROSS SAID ACCESS OPENING AND THROUGH SAID RETURN AIR DUCT AT A TEMPERATURE BELOW FREEZING, THE IMPROVEMENT COMPRISING MEANS FOR REDUCING THE ACCUMULATION OF FROST ON SAID EVAPORATOR COMPRISING A NON-REFRIGERATED FROST COLLECTOR LOCATED IN SAID RETURN AIR DUCT AND IN ADVANCE OF SAID EVAPORATOR FOR ACCUMULATING ON SAID FROST THEREON, MEANS FOR CONVERTING FROST ACCUMULATED ON SAID FROST COLLECTOR FROM A SOLID TO A LIQUID FROM WITHOUT SUBSTANTIAL VAPORIZATION OF THE LIQUID PRODUCED INCLUDING HEATING MEANS OPERABLE PERIODICALLY TO RAISE THE TEMPERATURE OF SAID FROST COLLECTOR TO A TEMPERATURE ABOVE FREEZING FOR A LIMITED TIME AND TO AN EXTENT SUFFICIENT ONLY TO CONVERT THE ACCUMULATED FROST INTO DROPS OF WATER WITHOUT CAUSING VAPORIZATION THEREOF AND MIGRATION OF MOISTURE FROM SAID FROST COLLECTOR TO SAID EVAPORATOR, SAID HEATING MEANS BEING OPERABLE AT LEAST AT TIMES DURING SAID REFRIGERATING CYCLE. 